CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to United States Provisional Patent Application Serial No. 63/362,917, filed April 13, 2022 and titled “AQUEOUS COATING COMPOSITIONS,” which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to an aqueous coating composition, a method of preparing an aqueous coating composition, and a porous substrate at least partially coated with an aqueous coating composition.

BACKGROUND

[0003] Coating compositions, such as stain compositions, for outdoor architectural components can not only enhance the aesthetic appearance of the components but also prevent or slow degradation of the components over time. Improving the outdoor durability of the coatings formed from such compositions improves their long-term ability to enhance and preserve the coated components.

SUMMARY

[0004] The present disclosure is directed to an aqueous coating composition including: water; a pigment and/or a UV absorber; and acrylic polymeric particles having an average particle size of from 1 to 500 nm dispersed in the water, where the coating composition includes at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition, where if the coating composition comprises the pigment, the coating composition has a pigment to binder ratio of up to 1:1, wherein the acrylic polymeric particles are formed by a two-stage process including: a first stage including forming an acrylic seed polymer; and a second stage including dispersing the seed polymer in the water and further reacting the seed polymer with ethylenically unsaturated monomers to form the acrylic polymeric particles.

[0005] The present disclosure is also directed to an aqueous coating composition including: a pigment and/or a UV absorber; and an aqueous dispersion including water, acrylic polymeric particles including particles of an addition polymer of ethylenically unsaturated monomers and a seed polymer of (i) a weak acid-containing monomer, (ii) a crosslinking monomer, and optionally (iii) a mono-ethylenically unsaturated monomer, where the acrylic polymeric particles have an average particle size of from 1 to 500 nm dispersed in the water, where the coating composition includes at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition, where if the coating composition comprises the pigment, the coating composition has a pigment to binder ratio of up to 1:1.

[0006] The present disclosure is also directed to a method of preparing an aqueous coating composition, including: preparing an aqueous dispersion including acrylic polymeric particles having an average particle size of from 1 to 500 nm formed by a two-stage process including: a first stage including forming an acrylic seed polymer; and a second stage including dispersing the seed polymer in water and further reacting the seed polymer with ethylenically unsaturated monomers to form the acrylic polymeric particles in the aqueous dispersion; and mixing a pigment and/or a UV absorber into the aqueous dispersion to form the coating composition, where the coating composition includes at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition, where if the coating composition comprises the pigment, the coating composition has a pigment to binder ratio of up to 1:1.

[0007] The present disclosure is also directed to a method of preparing an aqueous coating composition, including: preparing an aqueous dispersion including acrylic polymeric particles having an average particle size of from 1 to 500 nm, the aqueous dispersion including water, the acrylic polymeric particles including particles of an addition polymer of ethylenically unsaturated monomers and a seed polymer of (i) a weak acid-containing monomer, (ii) a crosslinking monomer, and optionally (iii) a mono-ethylenically unsaturated monomer; and mixing a pigment and/or a UV absorber into the aqueous dispersion to form the coating composition, wherein the coating composition includes at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition, where if the coating composition comprises the pigment, the coating composition has a pigment to binder ratio of up to 1:1.

DETAILED DESCRIPTION

[0008] For the purposes of the following detailed description, it is to be understood that the disclosed coating composition and methods may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. The term “about” may be taken to mean an amount, value or condition that deviates by less than 10%, less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the stated amount, value, or condition. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the presently disclosed coating composition. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0009] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosed coating composition are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard valuation found in their respective testing measurements.

[0010] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0011] In this application, the use of the singular includes the plural and the plural encompasses the singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. Further, in this application, the use of “a” or “an” means “at least one” unless specifically stated otherwise. For example, “a” pigment, “an” ethylenically unsaturated monomer, and the like refer to one or more of any of these items.

[0012] As used herein, a “film-forming resin” refers to a resin capable of forming a self- supporting continuous film on at least a horizontal surface of a substrate upon removal of any diluents or carriers present in the composition or upon curing. Also, as used herein, the term “polymer” is meant to refer to prepolymers, oligomers, and both homopolymers and copolymers. The term “resin” is used interchangeably with “polymer”.

[0013] As used herein, the transitional term “comprising” (and other comparable terms, e.g., “containing” and “including”) is “open-ended” and open to the inclusion of unspecified matter. Although described in terms of “comprising”, the terms “consisting essentially of’ and “consisting of’ are also within the scope of the disclosed coating composition.

[0014] Optionally, the aqueous coating composition disclosed herein is essentially free (i.e., substantially free) or completely free of components that are not specifically described. For example, the disclosed aqueous coating composition may optionally be essentially free or completely free of monomers, pigments, and/or crosslinking compounds not specifically disclosed herein. The aqueous coating composition may be “essentially free of’ a component where it includes only trace amounts and/or non-functional amounts of the component. For example, an such a component may be included in an amount no more than 1%, no more than 0.1%, or no more than 0.01% by total weight of the composition. An aqueous coating composition is “completely free of’ a component when it does not include a detectable amount of the component (i.e., does not include an amount above any inherent background signal associated with the testing instrument) when analyzed using standard coating composition analysis techniques such as, for example, chromatographic techniques (e.g., thin-layer chromatography (TLC), gas chromatography (GC), liquid chromatography (LC)), or spectroscopy techniques (e.g., Fourier transform infrared (FT1R) spectroscopy.

[0015] The present disclosure is directed to an aqueous coating composition comprising: water, a pigment and/or UV absorber; and acrylic polymeric particles having an average particle size of from 1 to 500 nm dispersed in the water.

[0016] The aqueous coating composition may comprise: water; a pigment and/or a UV absorber; and acrylic polymeric particles having an average particle size of from 1 to 500 nm dispersed in the water. The coating composition may comprise at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition. If the coating composition comprises the pigment, the coating composition may comprise a pigment to binder ratio of up to 1:1. The acrylic polymeric particles may be formed by a two-stage process comprising: a first stage comprising forming an acrylic seed polymer; and a second stage comprising dispersing the seed polymer in the water and further reacting the seed polymer with cthylcnically unsaturated monomers to form the acrylic polymeric particles.

[0017] The aqueous coating composition may comprise: a pigment and/or a UV absorber; and an aqueous dispersion comprising water, acrylic polymeric particles comprising particles of an addition polymer of ethylenically unsaturated monomers and a seed polymer of (i) a weak acidcontaining monomer, (ii) a crosslinking monomer, and optionally (iii) a mono-ethylenically unsaturated monomer. The acrylic polymeric particles may have an average particle size of from 1 to 500 nm dispersed in the water. The coating composition may comprise at least 15 weight percent of the acrylic polymeric particles, based on total resin solids of the coating composition. If the coating composition comprises the pigment, the coating composition may comprise a pigment to binder ratio of up to 1:1.

[0018] An aqueous coating composition refers to a composition comprising an aqueous medium. As used herein, an “aqueous medium” refers to a liquid medium comprising at least 50 weight percent water, based on the total weight of the liquid medium, where the liquid medium is defined as water and organic solvents which are liquid at ambient temperature (20-25 °C) and volatile at 110°C as measured by ASTM D2369-93. As such, it will be appreciated that the liquid medium basis does not include diluents which are liquid at ambient temperature but not volatile at 110°C as measured by ASTM D2369-93. Such aqueous liquid mediums can, for example, comprise at least 60 weight percent water, or at least 70 weight percent water, or at least 80 weight percent water, or at least 90 weight percent water, or at least 95 weight percent water, or 100 weight percent water, based on the total weight of the liquid medium. The solvents that, if present, make up less than 50 weight percent of the liquid medium include organic solvents. Non-limiting examples of suitable organic solvents include polar organic solvents, e.g. protic organic solvents such as glycols, glycol ether alcohols, alcohols, volatile ketones, glycol diethers, esters, and diesters. Other non-limiting examples of organic solvents include aromatic and aliphatic hydrocarbons.

[0019] The coating composition may comprise a pigment. The pigment may comprise a metal oxide pigment, such as iron oxide or titanium dioxide. The pigment may comprise a carbon black pigment. The pigment may comprise carbazole dioxazine crude pigment, azo, monoazo, diazo, naphthol AS, salt type (flakes), benzimidazolone, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazinc, triarylcarbonium, quinophthalonc, dikcto pyrrolo pyrrole red (“DPPBO red”) pigments, and/or mixtures thereof. The pigment may comprise dispersions of non-hiding, color-imparting organic pigment nanoparticles, which are available from PPG Industries, Inc. under the trademark ANDARO.

[0020] If the coating composition comprises the pigment, the coating composition may comprise a pigment to binder ratio of up to (which includes) 1:1, such as up to 0.6:1, up to 0.1:1, or up to 0.05 : 1. The coating composition may comprise a pigment to binder ratio of from greater than 0:1 to 1:1, such as from greater than 0:1 to 0.6:1, from greater than 0:1 to 0.1:1, or from greater than 0:1 to 0.05:1. The coating composition may be free of pigment (a pigment to binder ratio of 0:1). The acrylic polymeric particles form at least a part of the binder in the pigment to binder ratio.

[0021] The coating composition may comprise a UV absorber. Non-limiting commercially available examples of UV absorbers include propanoic acid,2-[4-[4,6-bis([l,T-biphenyl]-4-yl)- 1, 3, 5-triazin-2-yl]-3-hydroxyphenoxy]-, isooctyl ester (e.g., TINUVIN 479), P-[3-(2-H- benzotriazole-2-yl)-4-hydroxy-5-t-butylpheny l]-propionic acid-poly(ethylene glycol) 300 ester, bis { P-[3-(2-H-benzotriazole-2-yl)-4-hydroxy-5-t-butylphenyl]-pro pionic acid] -poly (ethylene glycol) 300 ester (e.g., TINUVIN 1130), UV absorbers based on a red shifted tris-resorcinol triazine chromophore (e.g., TINUVIN 477), 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2- hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-l ,3,5-triazine (e.g., TINUVIN 405), benzo tri azole- based UV absorbers (e.g., TINUVIN 99 DW), non-basic aminoether (e.g., TINUVIN 123 DW) (each available from BASF Resins available from BASF (Ludwigshafen, German)); and p- phenylenebis(methylenemalonic acid)tetraethyl ester (e.g., HOSTAVIN B-CAP), 2-ethyl,2'- ehtoxy-oxalanilide (e.g., HOSTAVIN VSU), and propanedioic acid,2-[(4- methoxyphenyl)methylene]-,l,3-dimethylester (e.g., HOSTAVIN PR-25) (each available from Clariant International Ltd. (Muttenz, Switzerland)). The UV absorber may be incorporated into the backbone of the acrylic polymeric particles (e.g., the acrylic seed polymer) or included as an additive component. UV absorbers incorporated into the backbone of the acrylic polymeric particles may be a UV reactive material, such as SILMER ACR DL50 (a linear di-functional acrylate-terminated silicone pre-polymer available from Siltech Corporation (Ontario, Canada)) or 2-[3-(2H-B enzotriazol-2 -y 1) -4 -hy droxypheny 1] ethyl methacrylate . [0022] When a UV absorber is included, the coating composition may comprise greater than 0 weight percent of the UV absorber, such as at least 1 weight percent, or at least 2 weight percent, based on total solids weight of the coating composition. The coating composition may comprise up to 10 weight percent of the UV absorber, such as up to 5 weight percent, based on total solids weight of the coating composition. The coating composition may comprise from greater than 0 to 10 weight percent of the UV absorber, such as from 1 to 5 weight percent, based on total solids weight of the coating composition.

[0023] The coating composition may comprise acrylic polymeric particles dispersed in the water. The acrylic polymeric particles may have an average particle size of from 1 to 500 nm, such as from 20 to 200 nm, from 50 to 150 nm, from 40 to 100 nm, or within a range using any combination of the foregoing values as endpoints. The acrylic polymeric particles may have an average particle size of up to 500 nm, such as up to 100 nm, or less than 100 nm. Particle size may be determined with a Zetasizer Nano ZS with measurement carried out at 25 °C. In an example, the particle dispersion was diluted to a weight solids content of 0.05% to 0.005% with ultra-pure water and the refractive index of the dispersed resin was specified as 1.59. The acrylic polymeric particles may have an average particle size smaller than a pore size of the substrate to which the coating composition is applied, such that the acrylic polymeric particles may penetrate the pores of the porous substrate.

[0024] The coating composition may comprise at least 15 weight percent of the acrylic polymeric particles, such as at least 20 weight percent, at least 30 weight percent, at least 40 weight percent, at least 50 weight percent, at least 70 weight percent, at least 80 weight percent, at least 90 weight percent, or 100 weight percent based on total resin solids of the coating composition. The coating composition may comprise up to 100 weight percent of the acrylic polymeric particles, such as up to 90 weight percent, up to 80 weight percent, up to 70 weight percent, up to 60 weight percent, up to 50 weight percent, up to 40 weight percent, up to 30 weight percent, up to 20 weight percent, or up to 15 weight percent based on total solids weight of the coating composition. The coating composition may comprise from 15 to 100 weight percent of the acrylic polymeric particles, such as from 20 to 90 weight percent, from 30 to 85 weight percent, from 40 to 80 weight percent, or from 50 to 75 weight percent based on total solids weight of the coating composition. [0025] The acrylic polymeric particles may be dispersed in water in the coating composition to form an aqueous dispersion of the acrylic polymeric particles. The acrylic polymeric particles may comprise particles of an addition polymer of ethylenically unsaturated monomers and a seed polymer of (i) a weak acid-containing monomer, (ii) a crosslinking monomer, and optionally (iii) a mono-ethylenically unsaturated monomer.

[0026] Regarding the seed polymer, the crosslinking monomer may react with the monomers of the weak acid-containing monomer and the optional mono-ethylenically unsaturated monomer to produce crosslinks and/or branches on the seed polymer. Non-limiting examples of the crosslinking monomer comprise ethylenically multi-unsaturated monomers having more than one ethlyenic unsaturation which can co-polymerize with the other ethylenically unsaturated comonomers so as to form the crosslinks and/or branches for the seed polymer. Non-limiting examples of such crosslinking co-monomers include allyl methacrylate, vinyl acrylate, divinyl benzene, ethylene glycol dimethacrylate, di-allyl phthalate, hexane diol diacrylate, trimethylol propane triacrylate, pentaerythritol triallyl ether, dicyclopentenyl oxyethyl methacrylate, glycerol triacrylate, and/or mixtures thereof. The crosslinking monomer may comprise two ethylenically unsaturated bonds.

[0027] The crosslinking monomer may comprise a mixture of two or more ethylenically singly- unsaturated monomers having a co-reactive functional group with another of the singly- unsaturated monomers, such that the co-reactive functional group on one monomer or polymer chain may react with the co-reactive functional group on the other monomer or polymer chain during polymerization to form crosslinks and/or branches of the seed polymer. Non-limiting examples of co-reactive functional groups on the ethylenically singly-unsaturated monomers comprise epoxy and carboxyl, anhydride and hydroxyl, isocyanate and hydroxyl, epoxy and hydroxyl, isocyanate and amine, acetoacetate and amine, and alkoxysilane and hydroxyl. Examples of suitable monomers having an epoxy group are glycidyl methacrylate and glycidyl acrylate. Suitable examples of monomers having carboxyl groups include (meth)acrylic acid and beta-carboxyethyl acrylate. An example of a suitable monomer having an anhydride group is maleic anhydride. Suitable examples of monomers having hydroxyl groups include hydroxyethyl (meth)acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl (meth)acrylate. An example of a monomer having an isocyanate group is 1-(1 -isocyanate- l-methylethyl)-3-(l -methylethenyl) benzene. A suitable example of a monomer containing an amine group is t-butylaminoethyl methacrylate. A suitable example of a monomer having an acetoacetate group is acetoacetoxyethyl (meth)acrylate. An example of a monomer having an alkoxysilane group is 3-(trimethoxysilyl) propyl (meth) acrylate.

[0028] The crosslinking monomer may comprise a mixture of ethylenically singly-unsaturated monomers having a co-reactive functional group and a multi-functional compound having two or more co-reactive functional groups and capable of reacting with the functional group of the monomer. Such multi-functional compounds are commonly referred to as crosslinking agents, and the multi-functional compounds may be free of ethylenic unsaturation so as to not copolymerize with the other ethylenically unsaturated co-monomers.

[0029] Examples of suitable crosslinking agents include polyisocyanates, aminoplast resins, epoxide resins, and/or mixtures thereof. Polyisocyanates may comprise compounds having two or more isocyanate groups per molecule. Non-limiting examples of diisocyanates include aliphatic or aromatic diisocyanates. Non-limiting examples of suitable aliphatic diisocyanates include hexamethylene diisocyanate, isophorone diisocyanate, and m-tetramethylxylene diisocyanate. Non-limiting examples of suitable aromatic diisocyanates include toluene diisocyanate and 4,4'- diphenylmethane diisocyanate. Other suitable polyisocyanates include the isocyanurate trimers, allophanates and uretdiones of diisocyanates such as those described above as well as the reaction products of these diisocyanates with polyols containing three or more hydroxyl groups. The aminoplast resins may include melamine formaldehyde and urea formaldehyde resins.

[0030] Non-limiting examples of ethylenically singly-unsaturated species capable of reacting with the polyisocyanate, melamine formaldehyde, and the urea formaldehyde crosslinking agents include hydroxy ethyl acrylate, hydroxy ethyl methacrylate, and hydroxy butyl acrylate; suitable non-limiting examples of ethylenically unsaturated species capable of reacting with the epoxide crosslinking agents include acrylic acid, methacrylic acid, and tertiary butyl amino ethyl methacrylate.

[0031] The crosslinking monomers may comprise from 0.3 to 10 weight percent of the seed polymer, such as from 0.5 to 8 weight percent, from 1 to 7 weight percent, or a range with endpoints selected from any combination of the foregoing values.

[0032] The weak acid-containing monomer may comprise weak acid groups. The weak acidcontaining monomer may comprise ethylenically unsaturated monomers having an acid group or its anhydride. Non-limiting examples of suitable weak acid-containing monomers include acrylic acid, methacrylic acid, beta carboxy ethyl acrylate, itaconic acid, crotonic acid, and/or mixtures thereof. Non-limiting examples of suitable ethylenically unsaturated acid anhydride containing monomers include succinic anhydride, maleic anhydride, methacrylic anhydride, and/or mixtures thereof. Other non-limiting examples of weak acid-containing monomers include initiators and chain transfer agents useful in polymerization reactions. Non-limiting examples of suitable weak acid-containing initiators include 4,4' azobis(4-cyano-pentanoic acid). Non-limiting examples of suitable weak acid-containing chain transfer agents include mercapto propionic acid and thioglycolic acid. The pKa of the weak acid-containing monomer may range from 3 to 6, such as from 4 to 5, as determined by the pKa values reported for each monomer from the 102 ^nd Edition of the CRC Handbook of Chemistry and Physics.

[0033] The weak acid-containing monomer may be generated after polymerization is substantially complete by reacting an acid anhydride with a hydroxyl group on the seed polymer. The hydroxyl group on the seed polymer can be provided by a hydroxyl containing monomer of the type mentioned above in relation to the crosslinking monomer. Suitable non-limiting examples of acid anhydride include trimellitic anhydride and phthalic anhydride.

[0034] The weak acid-containing monomer may comprise ethylenically unsaturated acid and/or acid anhydride monomers. The weak acid-containing monomer may comprise a carboxylic acid group or its anhydride.

[0035] The weak acid-containing monomer may comprise from 2 to 30 weight percent of the seed polymer, such as from 5 to 25 weight percent, from 6 to 20 weight percent, or a range with endpoints selected from any combination of the foregoing values.

[0036] The optional mono-ethylenically unsaturated monomer may comprise, as non-limiting examples, (meth)acrylic acid esters, amides and nitriles, vinyl monomers, vinyl esters, and/or mixtures thereof. The term “(meth) acrylic” refers to both acrylic and methacrylic.

[0037] Non-limiting examples of (meth)acrylic acid esters include alkyl esters, such as methyl (meth)acrylate, butyl (meth)acrylate, ethyl (meth) acrylate, ethylhexyl (meth) acrylate, propyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (methacrylate), glycidyl methacrylate, hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxypropyl (meth) acrylate, and poly(alkylene oxide) esters such as poly ethylene glycol methacrylate. Non-limiting examples of nitriles include (meth)acrylonitrile. Non-limiting examples of amide monomers include (meth) acrylamide. Non-limiting examples of vinyl monomers include styrene and alpha methyl styrene. Non-limiting examples of vinyl esters include vinyl Ci-4 alkanoate esters, such as vinyl acetate, vinyl propionate and vinyl butyrate; other vinyl esters include the vinyl versatates, which arc the vinyl esters of vcrsatic acid. Non-limiting examples of hydrophilic co-monomers include hydroxyethyl acrylate and alkoxy poly(oxyethylene) _n (meth) acrylate, in which the _n represents the molecular weight of the poly(oxyethylene) group and is typically from 500 to 3000.

[0038] The optional mono-ethylenically unsaturated monomer may comprise from 60 to 97.7 weight percent of the seed polymer, such as from 65 to 95 weight percent, from 70 to 90 weight percent, or a range with endpoints selected from any combination of the foregoing values.

[0039] The seed polymer may have a Mark Houwink alpha parameter of from 0.3 to 0.6, such as from 0.3 to 0.5, determined as described below.

[0040] The seed polymer may have a weight average molecular weight of at least 15,000, such as at least 20,000, at least 30,000, or at least 40,000. The seed polymer may have a weight average molecular weight of up to 80,000, such as up to 70,000, or up to 60,000. The seed polymer may have a weight average molecular weight of from 15,000 to 80,000, such as from 20,000 to 60,000, from 25,000 to 60,000, from 40,000 to 60,000, or a range with endpoints selected from any combination of the foregoing values. Number average molecular weight (Mn) and/or weight average molecular weight (Mw) and/or z-average molecular weight (Mz), as reported herein, was determined, unless otherwise indicated using size exclusion chromatography using a triple detector including a Waters 2695 separation module with a Wyatt Technology Light Scattering detector (miniDAWN), a differential refractive index detector (Optilab rEX)), and a Differential Viscometer detector (Viscostar). Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 ml min ¹ , and three PL Gel Mixed C columns were used for separation. Samples with solvent were vacuum dried (without heating) overnight prior to analysis. The performance of instrument was validated by a polystyrene standard of 30,000 Da. Polymer structure can be analyzed using a Mark- Houwink Log([r|]) vs. Log(M) plot. A fit of this data to the Mark-Houwink equation: [r|])= KM ^a , yields the parameter a characteristic of degree of branching.

[0041] The addition polymer of ethylenically unsaturated monomers may be formed from the following non-limiting examples of ethylenically unsaturated monomers: acid and/or acid anhydride monomers of the type useful in making the seed polymer, (meth)acrylic acid esters, amides and nitriles, vinyl monomers, vinyl esters and crosslinking monomers. Non-limiting examples of (meth)acrylic acid esters include alkyl esters, such as methyl (meth)acrylate, butyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, 2-ethyl hexyl acrylate and alkoxy poly(oxycthylcnc)n (mcth)acrylatc. Non-limiting examples of vinyl monomers include styrene and alpha methyl styrene. Non-limiting examples of vinyl esters include vinyl C alkanoate esters, such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl versatate. The monomers may also be a crosslinking monomer of the same type which are useful in making the seed polymer, which may be present in amounts of from 1 to 5 weight percent of the addition polymer of ethylenically unsaturated monomers.

[0042] The acrylic polymeric particles may be formed by a two-stage process comprising: (1) a first stage comprising an acrylic seed polymer comprising the seed polymer as previously described (formed of (i) a weak acid-containing monomer, (ii) a crosslinking monomer, and optionally (iii) a mono-ethylenically unsaturated monomer); and (2) a second stage comprising dispersing the seed polymer in the water and further reacting the seed polymer with ethylenically unsaturated monomers to form the acrylic polymeric particles. The ethylenically unsaturated monomers in the second stage may be those described in connection with the addition polymer of ethylenically unsaturated monomers. A portion of the seed polymer dispersed in the water may remain unreacted with the ethylenically unsaturated monomers, so as to include a mixture of the seed polymer and the reaction product of the seed polymer with the ethylenically unsaturated monomers (acrylic polymeric particles).

[0043] In the first stage, the seed polymer may be formed from a reaction of the (i) weak acidcontaining monomer, (ii) crosslinking monomer, and optional (iii) mono-ethylenically unsaturated monomer. The seed polymer may be formed using a free radical polymerization method carried out in a solvent and initiated using a free radical initiator at elevated temperature (relative to ambient temperature), such as from 70°C to 150°C or from 80°C to 140°C.

[0044] The seed polymer may be formed in the first stage in a non-aqueous medium to form a single phase solution. The non-aqueous medium may comprise an organic solvent that dissolves the seed polymer composition. The organic solvent may be a water miscible solvent. Non-limiting examples of suitable solvents may include 2-butoxy ethanol, propylene glycol monomethyl ether, 1-methoxy 2-propanol, 2,2,4-trimethyl 1,3 -pentanediol monoisobutyrate, n-butanol, and/or mixtures thereof.

[0045] The non-aqueous medium may comprise less than 50 weight percent water, based on the total weight of the liquid medium, such as less than 40 weight percent, less than 30 weight percent, less than 20 weight percent, less than 10 weight percent, less than 5 weight percent, or 0 weight percent. The amount of water in the non-aqueous medium may be less than an amount which would cause the composition of the first stage to no longer form a single phase solution.

[0046] Alternatively, the seed polymer may be formed substantially, essentially, and/or completely free of solvent. Substantially free of solvent means that the composition in the first stage comprises less than 20 weight percent solvent based on total resin solids of the composition in the first stage. Essentially free of solvent means that the composition in the first stage comprises less than 10 weight percent solvent based on total resin solids of the composition in the first stage. Completely free of solvent means that the composition in the first stage comprises 0 weight percent solvent based on total resin solids of the composition in the first stage.

[0047] A free radical initiator may be used in the reaction mixture in the first stage to form the seed polymer. Non-limiting examples of free radical initiators include peroxides, peresters and azobiscarbonitriles. Non-limiting examples of the peroxide initiators include hydrogen peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, benzoyl peroxide and di-t-amylperoxide. Non-limiting examples of the perester initiators include butylperoxy-2-ethyl hexanoate and t-butyl peracetate. A non-limiting example of a nitrile initiator is 2,2' azobis (2 methylbutyronitrile). Initiators containing acid groups can be used as described above in relation to the acid-containing species of the seed polymer. The amount of initiator used may range from 0.1 to 7 weight percent, based on monomers that form the seed polymer, such as from 0.5 to 5 weight percent or from 0.5 to 2 weight percent.

[0048] In the second stage, the ethylenically unsaturated monomers may be reacted with the seed polymer in an aqueous dispersion to grow the seed polymer and form the acrylic polymeric particles.

[0049] The seed polymer may be at least partially neutralized by the addition of a base prior to dispersion of the seed polymer into the water in the second stage. Non-limiting examples of suitable bases include alkali metal hydroxides and amines. Suitable amines include ammonia and primary, secondary, and tertiary amines such as triethylamine and dimethyl ethanolamine.

[0050] Following the addition of base, the solution of seed polymer may be added to water in a reactor vessel and the monomer mixture (including the ethylenically unsaturated monomers) introduced in the presence of a free radical polymerization initiator. The polymerization may be carried out by heating the mixture to a temperature of from 30°C to 98°C, such as from 40°C to 90°C.

[0051] Suitable polymerization initiators include peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide, persulphates such as potassium persulphate and ammonium persulphate, and redox initiator combinations such as ascorbic acid and hydrogen peroxide. Optionally, metal salts such as copper, chromium, and iron salts can be added when redox pairs are used.

[0052] In the second stage, the ethylenically unsaturated monomers reacted with the seed polymer may comprise hydrophobic monomers. Non-limiting examples of hydrophobic monomers include styrene, substituted styrenes (e.g. alpha-methyl styrene, vinyl toluene, t- butylstyrene), and alkyl esters of (meth) acrylic acid where the alkyl group contains four or more carbon atoms. Specific examples of such hydrophobic monomers include styrene, alpha-methyl styrene, isobornyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, n-butyl acrylate, n- butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, cyclohexyl methacrylate and lauryl methacrylate. The hydrophobic monomers may include from 50 to 70 weight percent of the ethylenically unsaturated monomers reacted with the seed polymer in the second stage.

[0053] The composition used to form the acrylic polymeric particles in the second stage may be substantially free, essentially free, and/or completely free of surfactant. Substantially free of surfactant means that the composition comprises less than 2 weight percent of surfactant based on total resin solids of the composition. Essentially free of surfactant means that the composition comprises less than 0.5 weight percent of surfactant based on total resin solids of the composition. Completely free of surfactant means that the composition comprises 0 weight percent of surfactant based on total resin solids of the composition. As such, the second stage is different from emulsion polymerization processes which require a composition including higher amounts of surfactant.

[0054] The acrylic polymeric polymers may be substantially /essentially free or completely free of olefin. An olefin refers to a hydrocarbon alkene monomer containing only carbon and hydrogen, but not including styrene monomers. Notwithstanding other definitions, substantially free of olefin means that the composition(s) used to form the acrylic polymeric particles comprise less than 5 weight percent of olefin monomers based on total resin solids of the composition(s). Essentially free of olefin means that the composition(s) used to form the acrylic polymeric particles comprise less than 1 weight percent of olefin monomers based on total resin solids of the composition(s). Completely free of olefin means that the composition(s) used to form the acrylic polymeric particles comprise 0 weight percent of olefin monomers based on total resin solids of the composition(s). The ratio of ethylenically unsaturated monomers to olefin monomers in the composition(s) used to form the acrylic polymeric particles may be greater than 1:1, based on total resin solids of the composition(s).

[0055] The acrylic polymeric particles may comprise an acid value of up to 60 mg KOH/g, such as up to 40 mg KOH/g or up to 25 mg KOH/g, based on total solids of the acrylic polymeric particles. The acrylic polymeric particles may comprise an acid value of at least 10 mg KOH/g, such as at least 15 mg KOH/g or at least 20 mg KOH/g, based on total solids of the acrylic polymeric particles. The acrylic polymeric particles may comprise an acid value of from 10 to 60 mg KOH/g, such as from 15 to 40 mg KOH/g, based on total solids of the acrylic polymeric particles. Acid values are determined using a Metrohm 798 MPT Titrino automatic titrator according to ASTM D 4662-15.

[0056] The coating composition may be prepared by preparing the aqueous dispersion comprising the acrylic polymeric particles having an average particle size of from 1 to 500 nm formed by the two-stage process comprising: the first stage comprising forming the acrylic seed polymer; and the second stage comprising dispersing the seed polymer in water and further reacting the seed polymer with the ethylenically unsaturated monomers to form the acrylic polymeric particles in the aqueous dispersion; and mixing the pigment and/or the UV absorber into the aqueous dispersion to form the coating composition.

[0057] The coating composition may be prepared by preparing the aqueous dispersion comprising the acrylic polymeric particles having an average particle size of from 1 to 500 nm, the aqueous dispersion comprising water, the acrylic polymeric particles comprising particles of the addition polymer of ethylenically unsaturated monomers and the seed polymer of (i) the weak acid-containing monomer, (ii) the crosslinking monomer, and optionally (iii) the mono- ethylenically unsaturated monomer; and mixing the pigment and/or the UV absorber into the aqueous dispersion to form the coating composition.

[0058] The coating composition may be applied to at least a portion of a substrate and dried and/or cured to form a coating layer over the substrate. The coating composition may be applied to a substrate by a suitable application method, such as brushing, roller application, and/or spraying methods, such as air-atomized spray, air-assisted spray, airless spray, high volume low pressure spray, and air-assisted airless spray.

[0059] The coating composition may form a non-hiding coating layer over the substrate. As used herein, the term “non-hiding coating layer” refers to a coating layer wherein, when deposited onto a surface, the surface beneath the coating layer is visible. The surface beneath the non-hiding coating layer may be visible when the non-hiding layer is applied at a dry film thickness of 0.5 to 5.0 mils (12.7 to 127 microns). One way to assess non-hiding is by measurement of opacity. As used herein, “opacity” refers to the degree to which a material obscures a substrate. “Percent opacity” refers herein to the ratio of the reflectance of a dry coating film over a black substrate of 5 percent or less reflectance, to the reflectance of the same coating film, equivalently applied and dried, over a substrate of 85 percent reflectance. The percent opacity of a dry coating film will depend on the dry film thickness of the coating and the concentration of color-imparting particles. The color-imparting non-hiding coating layer may have a percent opacity of no more than 90 percent, such as no more than 50 percent, at a dry film thickness of 1 mil (25 microns).

[0060] Non-limiting example of substrates include, but are not limited to, architectural substrates, such as metallic or non-metallic substrates including: concrete, stucco, cement board, MDF (medium density fiberboard) and particle board, gypsum board, wood, stone, metal, plastics, wall paper, textile, plaster, fiberglass, ceramic, etc., which may be pre-primed by waterborne or solvent borne primers. The architectural substrate may be wood, concrete, and/or stucco exposed to outdoor conditions. The substrate may be an outdoor architectural component, such as a deck, fence, siding, trim, and the like.

[0061] The substrate may include a base layer disposed beneath the coating formed from the coating composition. The base layer may be a weathered coating layer. As used herein, a weathered coating layer is defined as a coating layer that has been exposed to an outdoor environment for an extended period of time, such as at least 3 months, at least 6 months, at least 1 year, at least 2 years, or at least 5 years. As such, the coating formed from the coating composition, which is disposed over the weathered coating layer may be defined as a refinish coating layer (e.g., coating layer disposed over a weathered coating layer after a predefined time period).

[0062] The substrate may not include a base layer disposed thereover such that the coating composition is applied directly to the substrate itself. The coating composition may be the sole coating composition applied to the substrate. [0063] The substrate may be a porous substrate, such as paper, cardboard, particle board, fiber board, wood and wood products. Various woods that can be stained with the present compositions include, for example, oak and maple. These types of woods are used in the preparation of, for example, kitchen cabinets, bath cabinets, tables, desks, dressers, and other furniture. The porous substrate may have an average pore size in the range of from 1 nm to 500 microns, such as from 1 nm to 100 microns, or from 80 to 500 nm, as determined by mercury intrusion porosimetry (MIP). The porous substrate may have an average pore size of at least 1 nm, at least 20 nm, at least 50 nm, at least 80 nm, at least 300 nm, or at least 1 micron. The porous substrate may have an average pore size of at less than 500 microns, such as less than 100 microns, less than 500 nm, or less than 80 nm. The porous substrate may be a wood substrate having an average pore size of from 50 nm to 400 microns. The porous substrate may be a concrete substrate having an average pore size of from 25 nm to 170 nm. The porous substrate may be a paper substrate having an average pore size of from 0.3 microns to 0.5 microns.

[0064] The coating composition may be a stain composition which may penetrate the pores of the porous substrate such that at least a portion of the coating composition penetrates below the surface of the porous substrate. The “surface” of the substrate does not include the inner surface of the pores. The coating composition may penetrate at least 5 microns below the surface of the porous substrate, such as at least 10 microns, at least 20 microns, or at least 50 microns. The coating composition may penetrate from 5 to 175 microns below the surface of the porous substrate, such as from 10 to 150 microns. For soft grain wood regions (early wood), the coating composition may penetrate from 25 to 175 microns below the surface of the porous substrate. For hard grain wood regions (late wood), the coating composition may penetrate from 10 to 35 microns below the surface of the porous substrate. The coating composition may be used to coat a porous substrate by applying the coating composition to the porous substrate to penetrate the pores of the porous substrate, thereby protecting the porous substrate from environmental conditions, such as outdoor environmental conditions.

EXAMPLES

[0065] The following examples are presented to demonstrate general principles of the disclosed aqueous coating composition. The disclosure should not be considered as limited to the specific examples presented. Examples 1 and 2 Preparation of Acrylic Polymeric Particles

[0066] The acrylic polymeric particles of Examples 1 and 2 were prepared in the second stage (previously described in this disclosure) as follows. It is noted that the acrylic copolymer in Charge #1 was prepared according to the first stage previously described in this disclosure.

[0067] Charge #1 in Table 1 was first charged into a four-necked round bottom flask fitted with a thermocouple, mechanical stirrer and condenser, and then heated up to 50°C under a nitrogen blanket. Charge #2 was then added. When the temperature returned to 50°C, 10 weight percent of charge #3 was added into the flask over 5 minutes, and then 10 weight percent of Charge #4 was added into the flask over 5 minutes. The mixture was then held for 30 minutes. After 30 minutes' hold, the rest of Charge #3 and Charge #4 was fed into the flask over 3 hours. The reaction mixture was then held at 50°C for a further one hour before being cooled to room temperature (23°C). Amounts in Table 1 are in grams.

[0068] The acrylic polymeric particles of Example 1 had a solids content of 34.5%, an acid value of 16.1 mg KOH/g, and a z-average particle size of 52 nm as determined by the Zctasizcr. The acrylic polymeric particles of Example 2 had a solids content of 36.0%, an acid value of 15.9 mg KOH/g, and a z-average particle size of 93 nm as determined by the Zetasizer.

Table 1 ¹ The acrylic seed polymer, which is a copolymer of a-methyl styrene (10 weight percent), butyl methacrylate (21.4 weight percent), butyl acrylate (47.6 weight percent), hydroxy ethyl acrylate (10 weight percent), acrylic acid (7 weight percent) and allyl methacrylate (4 weight percent). Mn 2,580, Mw 40,400, Mz 316,000. Mark Houwink a parameter 0.36. 80.6% weight solids in Dowanol PM (l-methoxy-2-propanol available from Dow Chemical Company (Midland, MI))

² Linear di-functional acrylate-terminated silicone pre-polymer available from Siltech Corporation (Ontario, Canada)

³ 50 weight percent aqueous hydrogen peroxide solution

Examples 3-5 Preparation of Aqueous Coating Compositions

[0069] Aqueous coating compositions were prepared from the components listed in Table 2. The aqueous coating compositions were prepared by combining the components listed in Table 2 in a container and mixing the components. Amounts in Table 2 are in grams.

Table 2

⁴ A defoamer emulsion based on polycthcr siloxane technology, commercially available from Evonik Industries (Essen, Germany)

⁵ An aqueous solution of 1,2 benzisothiazolin-3-one at 19.3% active content, commercially available from Lonza-Monson Company (Basel, Switzerland) ⁶ A water-based fungicide dispersion of 20% TPBC (3-Todo-2-Propynyl Butyl Carbonate), commercially available from Troy Corporation (Florham Park, NJ)

⁷ An aqueous benzotriazole-based UV absorber dispersion, commercially available from BASF (Ludwigshafen, Germany)

⁸ An aqueous non-basic hindered amine light stabilizer (HALS), commercially available from BASF (Ludwigshafen, Germany)

⁹ An anionic surfactant, commercially available from Dow Chemical Company (Midland, MI)

¹⁰ An aqueous black pigment dispersion (34.4% pigment content by weight, 40.9% solids by weight), commercially available from Dystar (Singapore)

¹¹ An aqueous yellow pigment dispersion (25% pigment content by weight, 44% solids by weight), commercially available from Dystar (Singapore)

¹² An aqueous red pigment dispersion (35% pigment content by weight, 37.4% solids by weight), commercially available from Dystar (Singapore)

¹³ Yellow pigment dispersion, commercially available from PPG Industries, Inc. (Pittsburgh, PA)

¹⁴ Red pigment dispersion, commercially available from PPG Industries, Inc. (Pittsburgh, PA) [0070] The coating compositions of Examples 3-5 and four (4) commercially available stains, listed in Table 3, were applied by brush to 2x4 pressure treated lumber (PTL) decking that was cleaned with a bleach based deck cleaner and stripped with a caustic stripper prior to coating. The resulting decking coated with Examples 3-5 and the commercial stains were weathered horizontally in Allison Park, PA for at least 10 years.

[0071] After 10 years of exposure, the decking boards were evaluated for color retention, fade resistance, and erosion on a 0-10 rating scale, 10 being best. The results are shown in Table 3.

Table 3

[0072] The substrates coated with the coating compositions of Example 3-5 showed improved color retention, fade resistance, and less erosion compared to the substrates coated with the commercially available stains after 10 years of exposure, indicating that the coatings resulting from the coating compositions of Example 3-5 imparted improved overall durability compared to the commercially available stain compositions.

[0073] Whereas particular examples of this disclosure have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present disclosure may be made without departing from what is defined in the appended claims.